The present invention relates to computed tomography (CT) imaging apparatus; and more particularly, to the control of the x-ray source and data acquisition system during a scan.
In a current computed tomography system, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system, termed the "imaging plane". The x-ray beam passes through the object being imaged, such as a medical patient, and impinges upon an array of radiation detectors. The intensity of the transmitted radiation is dependent upon the attenuation of the x-ray beam by the object and each detector produces a separate electrical signal that is a measurement of the beam attenuation. The attenuation measurements from all the detectors are acquired separately and digitized by a data acquisition system to produce the transmission profile.
The x-ray source and detector array in a conventional CT system are rotated on a gantry within the imaging plane and around the object so that the angle at which the x-ray beam intersects the object constantly changes during a scan. A group of x-ray attenuation measurements from the detector array at a given angle is referred to as a "view" and a "scan" of the object comprises a set of views made at different angular orientations during one revolution of the x-ray source and detector. In a 2D scan, data is processed to construct an image that corresponds to a two dimensional slice taken through the object. The prevailing method for reconstructing an image from 2D data is referred to in the art as the filtered backprojection technique. This process converts the attenuation measurements from a scan into integers called "CT numbers" or "Hounsfield units", which are used to control the brightness of a corresponding pixel on a cathode ray tube display.
The operation of the x-ray generator and the acquisition system during a scan is controlled by a programmed computer. The operator prescribes a scan and in response to the prescribed scan parameters, the computer executes a program which controls the various elements of the CT imaging system to carry out the scan. The computer produces an output signal that repeatedly turns the x-ray source on and off as the gantry is rotated. It also produces an output signal that directs the data acquisition system to repeatedly sample the signals produced by the radiation detectors during the scan.
Modern CT imaging systems are called upon to conduct many different types of scans. For each of these different scans specific software is developed to operate system elements such as the x-ray source and the data acquisition system. Such software has become very complex and difficult to develop. This results from the increasingly complex and sophisticated scans that have been developed and from the increased demand for high speed scans.